It has long been desirable to achieve durable non-stick coatings on metal substrates that possess both excellent abrasion resistance and release. Non-stick coatings, especially for cookware, are well known in the art. Fluoropolymer resins are often used in these coatings, since these resins have a low surface energy as well as thermal and chemical resistance. Such polymers produce surfaces that release cooked food items, are cleaned easily, are stain resistant and are useful at cooking and baking temperatures. However, non-stick coatings based solely on fluoropolymer resins have poor adhesion to metal substrates. Thus, it has been a challenge to optimize a non-stick coating to achieve good adhesion to the substrate, good release of food particles in cooking applications, and good abrasion resistance to limit wear of the coating's surface.
Solutions to this problem, especially in the area of improved abrasion resistance, have been proposed in U.S. Pat. No. 6,291,054 B1 (Thomas et al); U.S. Pat. No. 6,592,977 (Thomas et al.); and U.S. Pat. No. 6,761,964 (Tannenbaum), which disclosures describe non-stick coating compositions and their applications to substrates to produce adherent, highly abrasion resistant coatings. These abrasion resistant coating compositions incorporate large ceramic particles, which can deflect abrasive forces away from the coating surface.
Abrasion resistance has also been addressed in WO 00/56537 (Gazo et al.), wherein non-stick coatings for use on aluminum substrates include a ceramic substrate incorporating abrasion resistant particles deposited on the aluminum surface with a fluoropolymer overcoat deposited over the ceramic substrate. Diamond particles are disclosed as a possible candidate for the abrasion resistant particles. The use of diamond particles in non-stick coatings on metal has been disclosed in EP 1 048 751 (Hort). In Hort, diamond particles which are known to have high thermal conductivity, are preferably incorporated into a hard base layer of aluminum oxide/titanium oxide, which is applied to the metal substrate prior to the application of the non-stick coating, to yield a very hard coating with good heat conductivity. Also disclosed is the incorporation of diamond particles in a layer of essentially fluorosilane, which is applied onto the hard base layer prior to the application of a cover layer of PTFE. Hort discloses that such a construction reduces the thermal barrier between the substrate and the non-stick coating and allows a more uniform temperature to be attained on the surface of the coated substrate.
Despite the teachings in recent disclosures that describe systems that attain increased abrasion resistance of non-stick coatings, there is still a desire to further improve the durability and wear resistance of coated substrates while maintaining good release.